In copending application Ser. No. 878,144, filed Feb. 15, 1978, by Miguel Angel Ondetti and Sesha Iyer Natarajan, now U.S. Pat. No. 4,129,566, there are described derivatives of 3,4-dehydroproline and 4,5-dehydropipecolic acid which have the formula ##STR5## wherein R and R.sub.2 each is hydrogen or lower alkyl;
These compounds, it will be observed, have a double bond between the second and third carbons from the nitrogen in a clockwise direction, carbons not attached to the carboxy group. These compounds are obtained from starting materials with the formula ##STR7##
The compounds of this invention are distinguishable by a double bond joining the carbon bearing the carboxy group and its adjacent carbon, carbons more distant from the nitrogen in a clockwise direction. Such compounds are not obtainable by the methods described in the prior application. We have found that the compounds of this invention can be obtained by a different route described below and furthermore similar R.sub.1 -substituted compounds of this description can be obtained whereas only ring unsubstituted compound of the prior type are available.